1. Field of the Invention
The present invention relates to a method for monitoring the surroundings of a running vehicle and a vehicle-mounted apparatus for carrying out the method, including a camera and a laser radar for detection of vehicles on the road and in the lane of the vehicle. The present invention also relates to a method for judging failure of the monitoring apparatus by detection of coincidence between the optical axes of the camera and the laser radar.
The instant application is based on Japanese Patent Application No. HEI 7-300214, filed Nov. 17, 1995, which is incorporated herein by reference for all purposes.
2. Brief Description of Related Art
As one of the conventional apparatuses of this type, Japanese Laid-Open Patent Publication (unexamined) No. 113482/1993 discloses a vehicle-mounted rear-end collision preventing apparatus. In this conventional apparatus, a laser radar of a single beam type, from which a laser beam is emitted in one direction in a defined narrow range ahead of a vehicle, is associated with an image processing means, whereby an obstacle ahead in the vehicle's own traffic lane is detected.
An object of this conventional apparatus is to detect an obstacle in the vehicle's own lane. However, if the road is curved ahead of the vehicle, the laser beam emitted from the vehicle's laser radar does not irradiate the vehicle's own lane, but irradiates an adjacent lane on either the left or the right side of the vehicle.
Accordingly, in case of a curved road, any obstacle ahead of the vehicle detected by the laser radar is not necessarily in the vehicle's own lane.
In view of the foregoing situation, in this conventional apparatus, first, an image ahead of a vehicle picked up by a camera is processed to detect the vehicle's own lane, and then the curvature ahead of the vehicle's own lane is detected. Then, direction of beam irradiation from the laser radar is adjusted in conformity with the curvature, whereby the laser beam correctly irradiates the vehicle's own lane at all times even though the road is curved ahead of the vehicle.
However, only a laser radar of single beam type for emitting a laser beam in one direction in a defined narrow range is described in the mentioned conventional art.
For the purpose of monitoring the surroundings of a running vehicle over a wider range, several systems for causing a laser beam to scan a wider range in the horizontal direction have been heretofore proposed.
For example, Japanese Patent Publication (examined) No.6349/1986 discloses a vehicle-mounted obstacle detecting apparatus. In this apparatus, a laser beam emitted in the running direction of a vehicle performs a two-dimensional scan, and reflected light from an obstacle is measured, whereby distance to the obstacle and the position thereof in the leftward or rightward direction are detected.
In the apparatus as disclosed in this Japanese patent publication, since it is intended to monitor not only the vehicle's own lane but also adjacent lanes over a wide range, it is possible to detect not only any obstacle in the vehicle's adjacent lanes but also any obstacle in other lanes further away from the vehicle.
In such a detection system there still remains the following problem. In a laser radar of the beam-scan type, since not only other vehicles running ahead in the vehicle's own lane but also other vehicles running in other lanes, including adjacent lanes, may be detected, it is absolutely essential to identify which of these vehicles represents an actual obstruction.
If the road is straight any other vehicle in the vehicle's own lane is running in front of the vehicle at all times. In this case, identification of another vehicle running ahead in the vehicle's own lane is very easy.
However, in reality no road is straight everywhere. On an ordinary road, another vehicle running ahead in a vehicle's own lane is not always in front of the vehicle. For example, where the road is curved rightward ahead of the vehicle, the other vehicle running ahead in the vehicle's own lane is on the right side of the vehicle.
On the other hand, where the road is curved leftward ahead of the vehicle, the other vehicle running ahead in the vehicle's own lane is on left side of the vehicle.
Moreover, depending upon the type of curve, there may be a case where another vehicle running in an adjacent lane is actually in front of the equipped vehicle.
Accordingly, with respect to a beam-scan type laser radar, it is certain that obstacles may be detected over a wider range, but it is difficult to judge what is a true obstacle in the vehicle's own lane.
Japanese Laid-Open Patent Publication (unexamined) No. 113482/1993 discloses a vehicle-mounted rear-end collision preventing apparatus in which the irradiation range of the laser beam is fixed. This allows for any obstacle ahead in the vehicle's own lane to be identified within a fixed range. In this apparatus, however, only an obstacle in the vehicle's own lane can be detected. Thus, the capability of the beam-scan type laser beam to monitor a wide range is not sufficiently utilized.